The present disclosure relates to superabrasive cutters with multiple cutting edges. Specifically, superabrasive cutters for rock drilling drag bits are described having two or more cutting points or edges that are formed into the outer periphery of the cutter.
Diamonds and cubic boron nitride (“CBN”) have been widely used as superabrasives on saws, drills, and other tools that utilize the superabrasive to cut, form, or polish other hard materials. Polycrystalline diamond (“PCD”) cutting elements are generally known. A PCD compact is a mass of diamond particles, bonded together to form an integral, tough, high-strength mass. Diamond or CBN particles may be bonded together as a compact in a particle-to-particle self-bonded relationship, optionally with a bonding medium disposed between the particles, such as a catalyzing material used to bond the abrasive particles together. For example, U.S. Pat. Nos. 3,236,615; 3,141,746; and 3,233,988, the disclosures of each of which are herein incorporated by reference in their entirety, describe PCD compacts and methods of forming the same.
An abrasive particle compact may be bonded to a substrate material, such as cemented tungsten carbide. Compacts of this type, bonded to a substrate are sometimes referred to as composite compacts, such as the compacts described in U.S. Pat. Nos. 3,743,489; 3,745,623; and 3,767,371, the disclosures of each of which are herein incorporated by reference in their entirety.
Composite compacts have found special utility as cutting elements in drill bits. Drill bits for use in rock drilling, machining of wear resistant materials, and other operations which require high abrasion resistance or wear resistance generally consist of a plurality of polycrystalline abrasive cutting elements fixed in a holder. For example, U.S. Pat. Nos. 4,109,737 and 5,374,854, the disclosures of each of which are herein incorporated by reference in their entirety, describe drill bits with a tungsten carbide substrate having a polycrystalline diamond compact on the outer surface of the cutting element.
A plurality of cutting elements may be mounted generally by interference fit or otherwise into recesses into the crown of a bit, such as a rotary drill bit. PCD is used as an abrasive wear and impact resistant surface in drilling, mining, and woodworking applications. PCD compacts have been designed to provide to both abrasion resistance and impact strength.
In addition, U.S. Pat. Nos. 5,848,657 and 6,196,340, the disclosures of each of which are incorporated herein by reference, describe dome cutters for roller cone bits. The cutters have a cone, dome, or hemispheric surface shape having grooves or ridges on the cutter surface formed on or about an otherwise non-planar shape. Such cutters are designed for rolling or spinning into a workpiece. In contrast, drag bits remove material by shearing the material and have contact at a single point, mostly at an edge of a planar cutter surface of the drag bit, rather than on the cutter surface itself. Therefore, grooves or ridges on the cutter surface of a drag bit would not be beneficial in cutting material.
Currently, the majority of PCD cutters are cylindrical in shape and have a cutting surface or diamond table or diamond layer that contacts the material to be cut. The PCD cutter generally has a diameter in the sizes of 13 mm, 16 mm, and 19 mm. Non-cylindrical cutters with sharp cutting points, known as scribe cutters, also have been described. In rock drilling drag bits 10, as shown in FIGS. 1A and 1B, either a cylindrical or a scribe cutter 11 may contact the rock 12 initially at a single point 13 and over a continuous surface area 14 as the cutter 11 wears in. The cutter 11 is thus “dragged” over the surface 14 of the material 12 to be cut and contacts the material at a point 13 that, as shown in FIG. 1B, grows into a wear plane 15 during use. As the cutter 11 wears, it forms a flat area 15 that becomes wider, but it still is initially a single point 13 of contact on the front of the diamond table.
Drag bits are constructed comprising various cutter sizes. Performance enhancements (rate of penetration and overall drilling depth) are sought by selecting PCD cutters with improvements in abrasion and/or impact performance among the sizes and shapes described above, and arranging them according to various bit design strategies.
The cost effectiveness of rock drilling drag bits incorporating PCD cutters may be determined by the bit's Rate of Penetration (ROP), which may be measured as a depth drilled over elapsed time (such as feet or meters per hour of operation) and lifetime of the PCD cutters and other bit components. Cutter lifetime is a function of the (1) abrasion resistance and (2) impact strength of the polycrystalline diamond material, in addition to the overall stability of the drill bit. Past efforts have demonstrated that increases in abrasion resistance are normally accompanied by decreases in impact strength. Consequently, reductions in cost effectiveness due to improved cutter materials have proven difficult to achieve. Therefore, many recent efforts have focused on improvements in drag bit design rather than on improved cutter design.
For example, U.S. Pat. No. 6,564,886, describes a bit design incorporating an arrangement of cutters with alternating positive and negative back rake angles; U.S. Pat. No. 5,551,522, describes a bit design incorporating an arrangement of cutters with different exposure height of various cutters; U.S. Pat. No. 5,582,261, describes a bit design incorporating an arrangement of cutters such that some cutters have greater initial exposure to the rock; U.S. Pat. No. 5,549,171, herein incorporated by reference in its entirety, describes a bit design incorporating the use of different back rake angles and scribe cutters; U.S. Pat. No. 5,383,527, describes a cutter design with an asymmetric support and an ovular; U.S. Pat. No. 5,607,024, describes a bit design incorporating cutters that contain areas with differing abrasion resistance, such as different grain sized PCD; and U.S. Pat. No. 5,607,025, describes a bit design incorporating overlapping large and small cylindrical PCD cutters. The disclosures of each of the forgoing references are incorporated herein by reference.
In the prior art, however, the problem of rate of penetration and bit stability are addressed by bit design, rather than cutter design. The bit designs incorporated multiple cutters into a drag bit design. Therefore, it is desirable to provide a cutter design resulting in increased cutter lifetime, rate of penetration, and drill bit stability without changing the material properties of the polycrystalline diamond material. A cutter design that accomplishes these goals through the design of the cutter itself, rather than through the design of a complex bit, is preferred. Such a cutter with improved rate of penetration, lifetime, and strength properties may be incorporated into any number of drill bit designs.
This application describes solutions for one or more of the problems described above.